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diff --git a/apps/plugins/puzzles/src/unfinished/numgame.c b/apps/plugins/puzzles/src/unfinished/numgame.c
new file mode 100644
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--- /dev/null
+++ b/apps/plugins/puzzles/src/unfinished/numgame.c
@@ -0,0 +1,1294 @@
+/*
+ * This program implements a breadth-first search which
+ * exhaustively solves the Countdown numbers game, and related
+ * games with slightly different rule sets such as `Flippo'.
+ * 
+ * Currently it is simply a standalone command-line utility to
+ * which you provide a set of numbers and it tells you everything
+ * it can make together with how many different ways it can be
+ * made. I would like ultimately to turn it into the generator for
+ * a Puzzles puzzle, but I haven't even started on writing a
+ * Puzzles user interface yet.
+ */
+
+/*
+ * TODO:
+ * 
+ *  - start thinking about difficulty ratings
+ *     + anything involving associative operations will be flagged
+ *       as many-paths because of the associative options (e.g.
+ *       2*3*4 can be (2*3)*4 or 2*(3*4), or indeed (2*4)*3). This
+ *       is probably a _good_ thing, since those are unusually
+ *       easy.
+ *     + tree-structured calculations ((a*b)/(c+d)) have multiple
+ *       paths because the independent branches of the tree can be
+ *       evaluated in either order, whereas straight-line
+ *       calculations with no branches will be considered easier.
+ *       Can we do anything about this? It's certainly not clear to
+ *       me that tree-structure calculations are _easier_, although
+ *       I'm also not convinced they're harder.
+ *     + I think for a realistic difficulty assessment we must also
+ *       consider the `obviousness' of the arithmetic operations in
+ *       some heuristic sense, and also (in Countdown) how many
+ *       numbers ended up being used.
+ *  - actually try some generations
+ *  - at this point we're probably ready to start on the Puzzles
+ *    integration.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <limits.h>
+#include <assert.h>
+#ifdef NO_TGMATH_H
+#  include <math.h>
+#else
+#  include <tgmath.h>
+#endif
+
+#include "puzzles.h"
+#include "tree234.h"
+
+/*
+ * To search for numbers we can make, we employ a breadth-first
+ * search across the space of sets of input numbers. That is, for
+ * example, we start with the set (3,6,25,50,75,100); we apply
+ * moves which involve combining two numbers (e.g. adding the 50
+ * and the 75 takes us to the set (3,6,25,100,125); and then we see
+ * if we ever end up with a set containing (say) 952.
+ * 
+ * If the rules are changed so that all the numbers must be used,
+ * this is easy to adjust to: we simply see if we end up with a set
+ * containing _only_ (say) 952.
+ * 
+ * Obviously, we can vary the rules about permitted arithmetic
+ * operations simply by altering the set of valid moves in the bfs.
+ * However, there's one common rule in this sort of puzzle which
+ * takes a little more thought, and that's _concatenation_. For
+ * example, if you are given (say) four 4s and required to make 10,
+ * you are permitted to combine two of the 4s into a 44 to begin
+ * with, making (44-4)/4 = 10. However, you are generally not
+ * allowed to concatenate two numbers that _weren't_ both in the
+ * original input set (you couldn't multiply two 4s to get 16 and
+ * then concatenate a 4 on to it to make 164), so concatenation is
+ * not an operation which is valid in all situations.
+ * 
+ * We could enforce this restriction by storing a flag alongside
+ * each number indicating whether or not it's an original number;
+ * the rules being that concatenation of two numbers is only valid
+ * if they both have the original flag, and that its output _also_
+ * has the original flag (so that you can concatenate three 4s into
+ * a 444), but that applying any other arithmetic operation clears
+ * the original flag on the output. However, we can get marginally
+ * simpler than that by observing that since concatenation has to
+ * happen to a number before any other operation, we can simply
+ * place all the concatenations at the start of the search. In
+ * other words, we have a global flag on an entire number _set_
+ * which indicates whether we are still permitted to perform
+ * concatenations; if so, we can concatenate any of the numbers in
+ * that set. Performing any other operation clears the flag.
+ */
+
+#define SETFLAG_CONCAT 1               /* we can do concatenation */
+
+struct sets;
+
+struct ancestor {
+    struct set *prev;                  /* index of ancestor set in set list */
+    unsigned char pa, pb, po, pr;      /* operation that got here from prev */
+};
+
+struct set {
+    int *numbers;                      /* rationals stored as n,d pairs */
+    short nnumbers;                    /* # of rationals, so half # of ints */
+    short flags;                       /* SETFLAG_CONCAT only, at present */
+    int npaths;                        /* number of ways to reach this set */
+    struct ancestor a;                 /* primary ancestor */
+    struct ancestor *as;               /* further ancestors, if we care */
+    int nas, assize;
+};
+
+struct output {
+    int number;
+    struct set *set;
+    int index;                         /* which number in the set is it? */
+    int npaths;                        /* number of ways to reach this */
+};
+
+#define SETLISTLEN 1024
+#define NUMBERLISTLEN 32768
+#define OUTPUTLISTLEN 1024
+struct operation;
+struct sets {
+    struct set **setlists;
+    int nsets, nsetlists, setlistsize;
+    tree234 *settree;
+    int **numberlists;
+    int nnumbers, nnumberlists, numberlistsize;
+    struct output **outputlists;
+    int noutputs, noutputlists, outputlistsize;
+    tree234 *outputtree;
+    const struct operation *const *ops;
+};
+
+#define OPFLAG_NEEDS_CONCAT 1
+#define OPFLAG_KEEPS_CONCAT 2
+#define OPFLAG_UNARY        4
+#define OPFLAG_UNARYPREFIX  8
+#define OPFLAG_FN           16
+
+struct operation {
+    /*
+     * Most operations should be shown in the output working, but
+     * concatenation should not; we just take the result of the
+     * concatenation and assume that it's obvious how it was
+     * derived.
+     */
+    int display;
+
+    /*
+     * Text display of the operator, in expressions and for
+     * debugging respectively.
+     */
+    const char *text, *dbgtext;
+
+    /*
+     * Flags dictating when the operator can be applied.
+     */
+    int flags;
+
+    /*
+     * Priority of the operator (for avoiding unnecessary
+     * parentheses when formatting it into a string).
+     */
+    int priority;
+
+    /*
+     * Associativity of the operator. Bit 0 means we need parens
+     * when the left operand of one of these operators is another
+     * instance of it, e.g. (2^3)^4. Bit 1 means we need parens
+     * when the right operand is another instance of the same
+     * operator, e.g. 2-(3-4). Thus:
+     * 
+     *  - this field is 0 for a fully associative operator, since
+     *    we never need parens.
+     *  - it's 1 for a right-associative operator.
+     *  - it's 2 for a left-associative operator.
+     *  - it's 3 for a _non_-associative operator (which always
+     *    uses parens just to be sure).
+     */
+    int assoc;
+
+    /*
+     * Whether the operator is commutative. Saves time in the
+     * search if we don't have to try it both ways round.
+     */
+    int commutes;
+
+    /*
+     * Function which implements the operator. Returns true on
+     * success, false on failure. Takes two rationals and writes
+     * out a third.
+     */
+    int (*perform)(int *a, int *b, int *output);
+};
+
+struct rules {
+    const struct operation *const *ops;
+    int use_all;
+};
+
+#define MUL(r, a, b) do { \
+    (r) = (a) * (b); \
+    if ((b) && (a) && (r) / (b) != (a)) return false; \
+} while (0)
+
+#define ADD(r, a, b) do { \
+    (r) = (a) + (b); \
+    if ((a) > 0 && (b) > 0 && (r) < 0) return false; \
+    if ((a) < 0 && (b) < 0 && (r) > 0) return false; \
+} while (0)
+
+#define OUT(output, n, d) do { \
+    int g = gcd((n),(d)); \
+    if (g < 0) g = -g; \
+    if ((d) < 0) g = -g; \
+    if (g == -1 && (n) < -INT_MAX) return false; \
+    if (g == -1 && (d) < -INT_MAX) return false; \
+    (output)[0] = (n)/g; \
+    (output)[1] = (d)/g; \
+    assert((output)[1] > 0); \
+} while (0)
+
+static int gcd(int x, int y)
+{
+    while (x != 0 && y != 0) {
+        int t = x;
+        x = y;
+        y = t % y;
+    }
+
+    return abs(x + y);                 /* i.e. whichever one isn't zero */
+}
+
+static int perform_add(int *a, int *b, int *output)
+{
+    int at, bt, tn, bn;
+    /*
+     * a0/a1 + b0/b1 = (a0*b1 + b0*a1) / (a1*b1)
+     */
+    MUL(at, a[0], b[1]);
+    MUL(bt, b[0], a[1]);
+    ADD(tn, at, bt);
+    MUL(bn, a[1], b[1]);
+    OUT(output, tn, bn);
+    return true;
+}
+
+static int perform_sub(int *a, int *b, int *output)
+{
+    int at, bt, tn, bn;
+    /*
+     * a0/a1 - b0/b1 = (a0*b1 - b0*a1) / (a1*b1)
+     */
+    MUL(at, a[0], b[1]);
+    MUL(bt, b[0], a[1]);
+    ADD(tn, at, -bt);
+    MUL(bn, a[1], b[1]);
+    OUT(output, tn, bn);
+    return true;
+}
+
+static int perform_mul(int *a, int *b, int *output)
+{
+    int tn, bn;
+    /*
+     * a0/a1 * b0/b1 = (a0*b0) / (a1*b1)
+     */
+    MUL(tn, a[0], b[0]);
+    MUL(bn, a[1], b[1]);
+    OUT(output, tn, bn);
+    return true;
+}
+
+static int perform_div(int *a, int *b, int *output)
+{
+    int tn, bn;
+
+    /*
+     * Division by zero is outlawed.
+     */
+    if (b[0] == 0)
+        return false;
+
+    /*
+     * a0/a1 / b0/b1 = (a0*b1) / (a1*b0)
+     */
+    MUL(tn, a[0], b[1]);
+    MUL(bn, a[1], b[0]);
+    OUT(output, tn, bn);
+    return true;
+}
+
+static int perform_exact_div(int *a, int *b, int *output)
+{
+    int tn, bn;
+
+    /*
+     * Division by zero is outlawed.
+     */
+    if (b[0] == 0)
+        return false;
+
+    /*
+     * a0/a1 / b0/b1 = (a0*b1) / (a1*b0)
+     */
+    MUL(tn, a[0], b[1]);
+    MUL(bn, a[1], b[0]);
+    OUT(output, tn, bn);
+
+    /*
+     * Exact division means we require the result to be an integer.
+     */
+    return (output[1] == 1);
+}
+
+static int max_p10(int n, int *p10_r)
+{
+    /*
+     * Find the smallest power of ten strictly greater than n.
+     *
+     * Special case: we must return at least 10, even if n is
+     * zero. (This is because this function is used for finding
+     * the power of ten by which to multiply a number being
+     * concatenated to the front of n, and concatenating 1 to 0
+     * should yield 10 and not 1.)
+     */
+    int p10 = 10;
+    while (p10 <= (INT_MAX/10) && p10 <= n)
+        p10 *= 10;
+    if (p10 > INT_MAX/10)
+        return false;                  /* integer overflow */
+    *p10_r = p10;
+    return true;
+}
+
+static int perform_concat(int *a, int *b, int *output)
+{
+    int t1, t2, p10;
+
+    /*
+     * We can't concatenate anything which isn't a non-negative
+     * integer.
+     */
+    if (a[1] != 1 || b[1] != 1 || a[0] < 0 || b[0] < 0)
+        return false;
+
+    /*
+     * For concatenation, we can safely assume leading zeroes
+     * aren't an issue. It isn't clear whether they `should' be
+     * allowed, but it turns out not to matter: concatenating a
+     * leading zero on to a number in order to harmlessly get rid
+     * of the zero is never necessary because unwanted zeroes can
+     * be disposed of by adding them to something instead. So we
+     * disallow them always.
+     *
+     * The only other possibility is that you might want to
+     * concatenate a leading zero on to something and then
+     * concatenate another non-zero digit on to _that_ (to make,
+     * for example, 106); but that's also unnecessary, because you
+     * can make 106 just as easily by concatenating the 0 on to the
+     * _end_ of the 1 first.
+     */
+    if (a[0] == 0)
+        return false;
+
+    if (!max_p10(b[0], &p10)) return false;
+
+    MUL(t1, p10, a[0]);
+    ADD(t2, t1, b[0]);
+    OUT(output, t2, 1);
+    return true;
+}
+
+#define IPOW(ret, x, y) do { \
+    int ipow_limit = (y); \
+    if ((x) == 1 || (x) == 0) ipow_limit = 1; \
+    else if ((x) == -1) ipow_limit &= 1; \
+    (ret) = 1; \
+    while (ipow_limit-- > 0) { \
+        int tmp; \
+        MUL(tmp, ret, x); \
+        ret = tmp; \
+    } \
+} while (0)
+
+static int perform_exp(int *a, int *b, int *output)
+{
+    int an, ad, xn, xd;
+
+    /*
+     * Exponentiation is permitted if the result is rational. This
+     * means that:
+     * 
+     *  - first we see whether we can take the (denominator-of-b)th
+     *    root of a and get a rational; if not, we give up.
+     * 
+     *  - then we do take that root of a
+     * 
+     *  - then we multiply by itself (numerator-of-b) times.
+     */
+    if (b[1] > 1) {
+        an = (int)(0.5 + pow(a[0], 1.0/b[1]));
+        ad = (int)(0.5 + pow(a[1], 1.0/b[1]));
+        IPOW(xn, an, b[1]);
+        IPOW(xd, ad, b[1]);
+        if (xn != a[0] || xd != a[1])
+            return false;
+    } else {
+        an = a[0];
+        ad = a[1];
+    }
+    if (b[0] >= 0) {
+        IPOW(xn, an, b[0]);
+        IPOW(xd, ad, b[0]);
+    } else {
+        IPOW(xd, an, -b[0]);
+        IPOW(xn, ad, -b[0]);
+    }
+    if (xd == 0)
+        return false;
+
+    OUT(output, xn, xd);
+    return true;
+}
+
+static int perform_factorial(int *a, int *b, int *output)
+{
+    int ret, t, i;
+
+    /*
+     * Factorials of non-negative integers are permitted.
+     */
+    if (a[1] != 1 || a[0] < 0)
+        return false;
+
+    /*
+     * However, a special case: we don't take a factorial of
+     * anything which would thereby remain the same.
+     */
+    if (a[0] == 1 || a[0] == 2)
+        return false;
+
+    ret = 1;
+    for (i = 1; i <= a[0]; i++) {
+        MUL(t, ret, i);
+        ret = t;
+    }
+
+    OUT(output, ret, 1);
+    return true;
+}
+
+static int perform_decimal(int *a, int *b, int *output)
+{
+    int p10;
+
+    /*
+     * Add a decimal digit to the front of a number;
+     * fail if it's not an integer.
+     * So, 1 --> 0.1, 15 --> 0.15,
+     * or, rather, 1 --> 1/10, 15 --> 15/100,
+     * x --> x / (smallest power of 10 > than x)
+     *
+     */
+    if (a[1] != 1) return false;
+
+    if (!max_p10(a[0], &p10)) return false;
+
+    OUT(output, a[0], p10);
+    return true;
+}
+
+static int perform_recur(int *a, int *b, int *output)
+{
+    int p10, tn, bn;
+
+    /*
+     * This converts a number like .4 to .44444..., or .45 to .45454...
+     * The input number must be -1 < a < 1.
+     *
+     * Calculate the smallest power of 10 that divides the denominator exactly,
+     * returning if no such power of 10 exists. Then multiply the numerator
+     * up accordingly, and the new denominator becomes that power of 10 - 1.
+     */
+    if (abs(a[0]) >= abs(a[1])) return false; /* -1 < a < 1 */
+
+    p10 = 10;
+    while (p10 <= (INT_MAX/10)) {
+        if ((a[1] <= p10) && (p10 % a[1]) == 0) goto found;
+        p10 *= 10;
+    }
+    return false;
+found:
+    tn = a[0] * (p10 / a[1]);
+    bn = p10 - 1;
+
+    OUT(output, tn, bn);
+    return true;
+}
+
+static int perform_root(int *a, int *b, int *output)
+{
+    /*
+     * A root B is: 1           iff a == 0
+     *              B ^ (1/A)   otherwise
+     */
+    int ainv[2], res;
+
+    if (a[0] == 0) {
+        OUT(output, 1, 1);
+        return true;
+    }
+
+    OUT(ainv, a[1], a[0]);
+    res = perform_exp(b, ainv, output);
+    return res;
+}
+
+static int perform_perc(int *a, int *b, int *output)
+{
+    if (a[0] == 0) return false; /* 0% = 0, uninteresting. */
+    if (a[1] > (INT_MAX/100)) return false;
+
+    OUT(output, a[0], a[1]*100);
+    return true;
+}
+
+static int perform_gamma(int *a, int *b, int *output)
+{
+    int asub1[2];
+
+    /*
+     * gamma(a) = (a-1)!
+     *
+     * special case not caught by perform_fact: gamma(1) is 1 so
+     * don't bother.
+     */
+    if (a[0] == 1 && a[1] == 1) return false;
+
+    OUT(asub1, a[0]-a[1], a[1]);
+    return perform_factorial(asub1, b, output);
+}
+
+static int perform_sqrt(int *a, int *b, int *output)
+{
+    int half[2] = { 1, 2 };
+
+    /*
+     * sqrt(0) == 0, sqrt(1) == 1: don't perform unary noops.
+     */
+    if (a[0] == 0 || (a[0] == 1 && a[1] == 1)) return false;
+
+    return perform_exp(a, half, output);
+}
+
+static const struct operation op_add = {
+    true, "+", "+", 0, 10, 0, true, perform_add
+};
+static const struct operation op_sub = {
+    true, "-", "-", 0, 10, 2, false, perform_sub
+};
+static const struct operation op_mul = {
+    true, "*", "*", 0, 20, 0, true, perform_mul
+};
+static const struct operation op_div = {
+    true, "/", "/", 0, 20, 2, false, perform_div
+};
+static const struct operation op_xdiv = {
+    true, "/", "/", 0, 20, 2, false, perform_exact_div
+};
+static const struct operation op_concat = {
+    false, "", "concat", OPFLAG_NEEDS_CONCAT | OPFLAG_KEEPS_CONCAT,
+        1000, 0, false, perform_concat
+};
+static const struct operation op_exp = {
+    true, "^", "^", 0, 30, 1, false, perform_exp
+};
+static const struct operation op_factorial = {
+    true, "!", "!", OPFLAG_UNARY, 40, 0, false, perform_factorial
+};
+static const struct operation op_decimal = {
+    true, ".", ".", OPFLAG_UNARY | OPFLAG_UNARYPREFIX | OPFLAG_NEEDS_CONCAT | OPFLAG_KEEPS_CONCAT, 50, 0, false, perform_decimal
+};
+static const struct operation op_recur = {
+    true, "...", "recur", OPFLAG_UNARY | OPFLAG_NEEDS_CONCAT, 45, 2, false, perform_recur
+};
+static const struct operation op_root = {
+    true, "v~", "root", 0, 30, 1, false, perform_root
+};
+static const struct operation op_perc = {
+    true, "%", "%", OPFLAG_UNARY | OPFLAG_NEEDS_CONCAT, 45, 1, false, perform_perc
+};
+static const struct operation op_gamma = {
+    true, "gamma", "gamma", OPFLAG_UNARY | OPFLAG_UNARYPREFIX | OPFLAG_FN, 1, 3, false, perform_gamma
+};
+static const struct operation op_sqrt = {
+    true, "v~", "sqrt", OPFLAG_UNARY | OPFLAG_UNARYPREFIX, 30, 1, false, perform_sqrt
+};
+
+/*
+ * In Countdown, divisions resulting in fractions are disallowed.
+ * http://www.askoxford.com/wordgames/countdown/rules/
+ */
+static const struct operation *const ops_countdown[] = {
+    &op_add, &op_mul, &op_sub, &op_xdiv, NULL
+};
+static const struct rules rules_countdown = {
+    ops_countdown, false
+};
+
+/*
+ * A slightly different rule set which handles the reasonably well
+ * known puzzle of making 24 using two 3s and two 8s. For this we
+ * need rational rather than integer division.
+ */
+static const struct operation *const ops_3388[] = {
+    &op_add, &op_mul, &op_sub, &op_div, NULL
+};
+static const struct rules rules_3388 = {
+    ops_3388, true
+};
+
+/*
+ * A still more permissive rule set usable for the four-4s problem
+ * and similar things. Permits concatenation.
+ */
+static const struct operation *const ops_four4s[] = {
+    &op_add, &op_mul, &op_sub, &op_div, &op_concat, NULL
+};
+static const struct rules rules_four4s = {
+    ops_four4s, true
+};
+
+/*
+ * The most permissive ruleset I can think of. Permits
+ * exponentiation, and also silly unary operators like factorials.
+ */
+static const struct operation *const ops_anythinggoes[] = {
+    &op_add, &op_mul, &op_sub, &op_div, &op_concat, &op_exp, &op_factorial, 
+    &op_decimal, &op_recur, &op_root, &op_perc, &op_gamma, &op_sqrt, NULL
+};
+static const struct rules rules_anythinggoes = {
+    ops_anythinggoes, true
+};
+
+#define ratcmp(a,op,b) ( (long long)(a)[0] * (b)[1] op \
+                         (long long)(b)[0] * (a)[1] )
+
+static int addtoset(struct set *set, int newnumber[2])
+{
+    int i, j;
+
+    /* Find where we want to insert the new number */
+    for (i = 0; i < set->nnumbers &&
+         ratcmp(set->numbers+2*i, <, newnumber); i++);
+
+    /* Move everything else up */
+    for (j = set->nnumbers; j > i; j--) {
+        set->numbers[2*j] = set->numbers[2*j-2];
+        set->numbers[2*j+1] = set->numbers[2*j-1];
+    }
+
+    /* Insert the new number */
+    set->numbers[2*i] = newnumber[0];
+    set->numbers[2*i+1] = newnumber[1];
+
+    set->nnumbers++;
+
+    return i;
+}
+
+#define ensure(array, size, newlen, type) do { \
+    if ((newlen) > (size)) { \
+        (size) = (newlen) + 512; \
+        (array) = sresize((array), (size), type); \
+    } \
+} while (0)
+
+static int setcmp(void *av, void *bv)
+{
+    struct set *a = (struct set *)av;
+    struct set *b = (struct set *)bv;
+    int i;
+
+    if (a->nnumbers < b->nnumbers)
+        return -1;
+    else if (a->nnumbers > b->nnumbers)
+        return +1;
+
+    if (a->flags < b->flags)
+        return -1;
+    else if (a->flags > b->flags)
+        return +1;
+
+    for (i = 0; i < a->nnumbers; i++) {
+        if (ratcmp(a->numbers+2*i, <, b->numbers+2*i))
+            return -1;
+        else if (ratcmp(a->numbers+2*i, >, b->numbers+2*i))
+            return +1;
+    }
+
+    return 0;
+}
+
+static int outputcmp(void *av, void *bv)
+{
+    struct output *a = (struct output *)av;
+    struct output *b = (struct output *)bv;
+
+    if (a->number < b->number)
+        return -1;
+    else if (a->number > b->number)
+        return +1;
+
+    return 0;
+}
+
+static int outputfindcmp(void *av, void *bv)
+{
+    int *a = (int *)av;
+    struct output *b = (struct output *)bv;
+
+    if (*a < b->number)
+        return -1;
+    else if (*a > b->number)
+        return +1;
+
+    return 0;
+}
+
+static void addset(struct sets *s, struct set *set, int multiple,
+                   struct set *prev, int pa, int po, int pb, int pr)
+{
+    struct set *s2;
+    int npaths = (prev ? prev->npaths : 1);
+
+    assert(set == s->setlists[s->nsets / SETLISTLEN] + s->nsets % SETLISTLEN);
+    s2 = add234(s->settree, set);
+    if (s2 == set) {
+        /*
+         * New set added to the tree.
+         */
+        set->a.prev = prev;
+        set->a.pa = pa;
+        set->a.po = po;
+        set->a.pb = pb;
+        set->a.pr = pr;
+        set->npaths = npaths;
+        s->nsets++;
+        s->nnumbers += 2 * set->nnumbers;
+        set->as = NULL;
+        set->nas = set->assize = 0;
+    } else {
+        /*
+         * Rediscovered an existing set. Update its npaths.
+         */
+        s2->npaths += npaths;
+        /*
+         * And optionally enter it as an additional ancestor.
+         */
+        if (multiple) {
+            if (s2->nas >= s2->assize) {
+                s2->assize = s2->nas * 3 / 2 + 4;
+                s2->as = sresize(s2->as, s2->assize, struct ancestor);
+            }
+            s2->as[s2->nas].prev = prev;
+            s2->as[s2->nas].pa = pa;
+            s2->as[s2->nas].po = po;
+            s2->as[s2->nas].pb = pb;
+            s2->as[s2->nas].pr = pr;
+            s2->nas++;
+        }
+    }
+}
+
+static struct set *newset(struct sets *s, int nnumbers, int flags)
+{
+    struct set *sn;
+
+    ensure(s->setlists, s->setlistsize, s->nsets/SETLISTLEN+1, struct set *);
+    while (s->nsetlists <= s->nsets / SETLISTLEN)
+        s->setlists[s->nsetlists++] = snewn(SETLISTLEN, struct set);
+    sn = s->setlists[s->nsets / SETLISTLEN] + s->nsets % SETLISTLEN;
+
+    if (s->nnumbers + nnumbers * 2 > s->nnumberlists * NUMBERLISTLEN)
+        s->nnumbers = s->nnumberlists * NUMBERLISTLEN;
+    ensure(s->numberlists, s->numberlistsize,
+           s->nnumbers/NUMBERLISTLEN+1, int *);
+    while (s->nnumberlists <= s->nnumbers / NUMBERLISTLEN)
+        s->numberlists[s->nnumberlists++] = snewn(NUMBERLISTLEN, int);
+    sn->numbers = s->numberlists[s->nnumbers / NUMBERLISTLEN] +
+        s->nnumbers % NUMBERLISTLEN;
+
+    /*
+     * Start the set off empty.
+     */
+    sn->nnumbers = 0;
+
+    sn->flags = flags;
+
+    return sn;
+}
+
+static int addoutput(struct sets *s, struct set *ss, int index, int *n)
+{
+    struct output *o, *o2;
+
+    /*
+     * Target numbers are always integers.
+     */
+    if (ss->numbers[2*index+1] != 1)
+        return false;
+
+    ensure(s->outputlists, s->outputlistsize, s->noutputs/OUTPUTLISTLEN+1,
+           struct output *);
+    while (s->noutputlists <= s->noutputs / OUTPUTLISTLEN)
+        s->outputlists[s->noutputlists++] = snewn(OUTPUTLISTLEN,
+                                                  struct output);
+    o = s->outputlists[s->noutputs / OUTPUTLISTLEN] +
+        s->noutputs % OUTPUTLISTLEN;
+
+    o->number = ss->numbers[2*index];
+    o->set = ss;
+    o->index = index;
+    o->npaths = ss->npaths;
+    o2 = add234(s->outputtree, o);
+    if (o2 != o) {
+        o2->npaths += o->npaths;
+    } else {
+        s->noutputs++;
+    }
+    *n = o->number;
+    return true;
+}
+
+static struct sets *do_search(int ninputs, int *inputs,
+                              const struct rules *rules, int *target,
+                              int debug, int multiple)
+{
+    struct sets *s;
+    struct set *sn;
+    int qpos, i;
+    const struct operation *const *ops = rules->ops;
+
+    s = snew(struct sets);
+    s->setlists = NULL;
+    s->nsets = s->nsetlists = s->setlistsize = 0;
+    s->numberlists = NULL;
+    s->nnumbers = s->nnumberlists = s->numberlistsize = 0;
+    s->outputlists = NULL;
+    s->noutputs = s->noutputlists = s->outputlistsize = 0;
+    s->settree = newtree234(setcmp);
+    s->outputtree = newtree234(outputcmp);
+    s->ops = ops;
+
+    /*
+     * Start with the input set.
+     */
+    sn = newset(s, ninputs, SETFLAG_CONCAT);
+    for (i = 0; i < ninputs; i++) {
+        int newnumber[2];
+        newnumber[0] = inputs[i];
+        newnumber[1] = 1;
+        addtoset(sn, newnumber);
+    }
+    addset(s, sn, multiple, NULL, 0, 0, 0, 0);
+
+    /*
+     * Now perform the breadth-first search: keep looping over sets
+     * until we run out of steam.
+     */
+    qpos = 0;
+    while (qpos < s->nsets) {
+        struct set *ss = s->setlists[qpos / SETLISTLEN] + qpos % SETLISTLEN;
+        struct set *sn;
+        int i, j, k, m;
+
+        if (debug) {
+            int i;
+            printf("processing set:");
+            for (i = 0; i < ss->nnumbers; i++) {
+                printf(" %d", ss->numbers[2*i]);
+                if (ss->numbers[2*i+1] != 1)
+                    printf("/%d", ss->numbers[2*i+1]);
+            }
+            printf("\n");
+        }
+
+        /*
+         * Record all the valid output numbers in this state. We
+         * can always do this if there's only one number in the
+         * state; otherwise, we can only do it if we aren't
+         * required to use all the numbers in coming to our answer.
+         */
+        if (ss->nnumbers == 1 || !rules->use_all) {
+            for (i = 0; i < ss->nnumbers; i++) {
+                int n;
+
+                if (addoutput(s, ss, i, &n) && target && n == *target)
+                    return s;
+            }
+        }
+
+        /*
+         * Try every possible operation from this state.
+         */
+        for (k = 0; ops[k] && ops[k]->perform; k++) {
+            if ((ops[k]->flags & OPFLAG_NEEDS_CONCAT) &&
+                !(ss->flags & SETFLAG_CONCAT))
+                continue;              /* can't use this operation here */
+            for (i = 0; i < ss->nnumbers; i++) {
+                int jlimit = (ops[k]->flags & OPFLAG_UNARY ? 1 : ss->nnumbers);
+                for (j = 0; j < jlimit; j++) {
+                    int n[2], newnn = ss->nnumbers;
+                    int pa, po, pb, pr;
+
+                    if (!(ops[k]->flags & OPFLAG_UNARY)) {
+                        if (i == j)
+                            continue;  /* can't combine a number with itself */
+                        if (i > j && ops[k]->commutes)
+                            continue;  /* no need to do this both ways round */
+                        newnn--;
+                    }
+                    if (!ops[k]->perform(ss->numbers+2*i, ss->numbers+2*j, n))
+                        continue;      /* operation failed */
+
+                    sn = newset(s, newnn, ss->flags);
+
+                    if (!(ops[k]->flags & OPFLAG_KEEPS_CONCAT))
+                        sn->flags &= ~SETFLAG_CONCAT;
+
+                    for (m = 0; m < ss->nnumbers; m++) {
+                        if (m == i || (!(ops[k]->flags & OPFLAG_UNARY) &&
+                                       m == j))
+                            continue;
+                        sn->numbers[2*sn->nnumbers] = ss->numbers[2*m];
+                        sn->numbers[2*sn->nnumbers + 1] = ss->numbers[2*m + 1];
+                        sn->nnumbers++;
+                    }
+                    pa = i;
+                    if (ops[k]->flags & OPFLAG_UNARY)
+                        pb = sn->nnumbers+10;
+                    else
+                        pb = j;
+                    po = k;
+                    pr = addtoset(sn, n);
+                    addset(s, sn, multiple, ss, pa, po, pb, pr);
+                    if (debug) {
+                        int i;
+                        if (ops[k]->flags & OPFLAG_UNARYPREFIX)
+                            printf("  %s %d ->", ops[po]->dbgtext, pa);
+                        else if (ops[k]->flags & OPFLAG_UNARY)
+                            printf("  %d %s ->", pa, ops[po]->dbgtext);
+                        else
+                            printf("  %d %s %d ->", pa, ops[po]->dbgtext, pb);
+                        for (i = 0; i < sn->nnumbers; i++) {
+                            printf(" %d", sn->numbers[2*i]);
+                            if (sn->numbers[2*i+1] != 1)
+                                printf("/%d", sn->numbers[2*i+1]);
+                        }
+                        printf("\n");
+                    }
+                }
+            }
+        }
+
+        qpos++;
+    }
+
+    return s;
+}
+
+static void free_sets(struct sets *s)
+{
+    int i;
+
+    freetree234(s->settree);
+    freetree234(s->outputtree);
+    for (i = 0; i < s->nsetlists; i++)
+        sfree(s->setlists[i]);
+    sfree(s->setlists);
+    for (i = 0; i < s->nnumberlists; i++)
+        sfree(s->numberlists[i]);
+    sfree(s->numberlists);
+    for (i = 0; i < s->noutputlists; i++)
+        sfree(s->outputlists[i]);
+    sfree(s->outputlists);
+    sfree(s);
+}
+
+/*
+ * Print a text formula for producing a given output.
+ */
+static void print_recurse(struct sets *s, struct set *ss, int pathindex,
+                          int index, int priority, int assoc, int child);
+static void print_recurse_inner(struct sets *s, struct set *ss,
+                                struct ancestor *a, int pathindex, int index,
+                                int priority, int assoc, int child)
+{
+    if (a->prev && index != a->pr) {
+        int pi;
+
+        /*
+         * This number was passed straight down from this set's
+         * predecessor. Find its index in the previous set and
+         * recurse to there.
+         */
+        pi = index;
+        assert(pi != a->pr);
+        if (pi > a->pr)
+            pi--;
+        if (pi >= min(a->pa, a->pb)) {
+            pi++;
+            if (pi >= max(a->pa, a->pb))
+                pi++;
+        }
+        print_recurse(s, a->prev, pathindex, pi, priority, assoc, child);
+    } else if (a->prev && index == a->pr &&
+               s->ops[a->po]->display) {
+        /*
+         * This number was created by a displayed operator in the
+         * transition from this set to its predecessor. Hence we
+         * write an open paren, then recurse into the first
+         * operand, then write the operator, then the second
+         * operand, and finally close the paren.
+         */
+        const char *op;
+        int parens, thispri, thisassoc;
+
+        /*
+         * Determine whether we need parentheses.
+         */
+        thispri = s->ops[a->po]->priority;
+        thisassoc = s->ops[a->po]->assoc;
+        parens = (thispri < priority ||
+                  (thispri == priority && (assoc & child)));
+
+        if (parens)
+            putchar('(');
+
+        if (s->ops[a->po]->flags & OPFLAG_UNARYPREFIX)
+            for (op = s->ops[a->po]->text; *op; op++)
+                putchar(*op);
+
+        if (s->ops[a->po]->flags & OPFLAG_FN)
+            putchar('(');
+
+        print_recurse(s, a->prev, pathindex, a->pa, thispri, thisassoc, 1);
+
+        if (s->ops[a->po]->flags & OPFLAG_FN)
+            putchar(')');
+
+        if (!(s->ops[a->po]->flags & OPFLAG_UNARYPREFIX))
+            for (op = s->ops[a->po]->text; *op; op++)
+                putchar(*op);
+
+        if (!(s->ops[a->po]->flags & OPFLAG_UNARY))
+            print_recurse(s, a->prev, pathindex, a->pb, thispri, thisassoc, 2);
+
+        if (parens)
+            putchar(')');
+    } else {
+        /*
+         * This number is either an original, or something formed
+         * by a non-displayed operator (concatenation). Either way,
+         * we display it as is.
+         */
+        printf("%d", ss->numbers[2*index]);
+        if (ss->numbers[2*index+1] != 1)
+            printf("/%d", ss->numbers[2*index+1]);
+    }
+}
+static void print_recurse(struct sets *s, struct set *ss, int pathindex,
+                          int index, int priority, int assoc, int child)
+{
+    if (!ss->a.prev || pathindex < ss->a.prev->npaths) {
+        print_recurse_inner(s, ss, &ss->a, pathindex,
+                            index, priority, assoc, child);
+    } else {
+        int i;
+        pathindex -= ss->a.prev->npaths;
+        for (i = 0; i < ss->nas; i++) {
+            if (pathindex < ss->as[i].prev->npaths) {
+                print_recurse_inner(s, ss, &ss->as[i], pathindex,
+                                    index, priority, assoc, child);
+                break;
+            }
+            pathindex -= ss->as[i].prev->npaths;
+        }
+    }
+}
+static void print(int pathindex, struct sets *s, struct output *o)
+{
+    print_recurse(s, o->set, pathindex, o->index, 0, 0, 0);
+}
+
+/*
+ * gcc -g -O0 -o numgame numgame.c -I.. ../{malloc,tree234,nullfe}.c -lm
+ */
+int main(int argc, char **argv)
+{
+    int doing_opts = true;
+    const struct rules *rules = NULL;
+    char *pname = argv[0];
+    int got_target = false, target = 0;
+    int numbers[10], nnumbers = 0;
+    int verbose = false;
+    int pathcounts = false;
+    int multiple = false;
+    int debug_bfs = false;
+    int got_range = false, rangemin = 0, rangemax = 0;
+
+    struct output *o;
+    struct sets *s;
+    int i, start, limit;
+
+    while (--argc) {
+        char *p = *++argv;
+        int c;
+
+        if (doing_opts && *p == '-') {
+            p++;
+
+            if (!strcmp(p, "-")) {
+                doing_opts = false;
+                continue;
+            } else if (*p == '-') {
+                p++;
+                if (!strcmp(p, "debug-bfs")) {
+                    debug_bfs = true;
+                } else {
+                    fprintf(stderr, "%s: option '--%s' not recognised\n",
+                            pname, p);
+                }
+            } else while (p && *p) switch (c = *p++) {
+              case 'C':
+                rules = &rules_countdown;
+                break;
+              case 'B':
+                rules = &rules_3388;
+                break;
+              case 'D':
+                rules = &rules_four4s;
+                break;
+              case 'A':
+                rules = &rules_anythinggoes;
+                break;
+              case 'v':
+                verbose = true;
+                break;
+              case 'p':
+                pathcounts = true;
+                break;
+              case 'm':
+                multiple = true;
+                break;
+              case 't':
+              case 'r':
+                {
+                    char *v;
+                    if (*p) {
+                        v = p;
+                        p = NULL;
+                    } else if (--argc) {
+                        v = *++argv;
+                    } else {
+                        fprintf(stderr, "%s: option '-%c' expects an"
+                                " argument\n", pname, c);
+                        return 1;
+                    }
+                    switch (c) {
+                      case 't':
+                        got_target = true;
+                        target = atoi(v);
+                        break;
+                      case 'r':
+                        {
+                             char *sep = strchr(v, '-');
+                             got_range = true;
+                             if (sep) {
+                                 rangemin = atoi(v);
+                                 rangemax = atoi(sep+1);
+                             } else {
+                                 rangemin = 0;
+                                 rangemax = atoi(v);
+                             }
+                        }
+                        break;
+                    }
+                }
+                break;
+              default:
+                fprintf(stderr, "%s: option '-%c' not"
+                        " recognised\n", pname, c);
+                return 1;
+            }
+        } else {
+            if (nnumbers >= lenof(numbers)) {
+                fprintf(stderr, "%s: internal limit of %d numbers exceeded\n",
+                        pname, (int)lenof(numbers));
+                return 1;
+            } else {
+                numbers[nnumbers++] = atoi(p);
+            }
+        }
+    }
+
+    if (!rules) {
+        fprintf(stderr, "%s: no rule set specified; use -C,-B,-D,-A\n", pname);
+        return 1;
+    }
+
+    if (!nnumbers) {
+        fprintf(stderr, "%s: no input numbers specified\n", pname);
+        return 1;
+    }
+
+    if (got_range) {
+        if (got_target) {
+            fprintf(stderr, "%s: only one of -t and -r may be specified\n", pname);
+            return 1;
+        }
+        if (rangemin >= rangemax) {
+            fprintf(stderr, "%s: range not sensible (%d - %d)\n", pname, rangemin, rangemax);
+            return 1;
+        }
+    }
+
+    s = do_search(nnumbers, numbers, rules, (got_target ? &target : NULL),
+                  debug_bfs, multiple);
+
+    if (got_target) {
+        o = findrelpos234(s->outputtree, &target, outputfindcmp,
+                          REL234_LE, &start);
+        if (!o)
+            start = -1;
+        o = findrelpos234(s->outputtree, &target, outputfindcmp,
+                          REL234_GE, &limit);
+        if (!o)
+            limit = -1;
+        assert(start != -1 || limit != -1);
+        if (start == -1)
+            start = limit;
+        else if (limit == -1)
+            limit = start;
+        limit++;
+    } else if (got_range) {
+        if (!findrelpos234(s->outputtree, &rangemin, outputfindcmp,
+                           REL234_GE, &start) ||
+            !findrelpos234(s->outputtree, &rangemax, outputfindcmp,
+                           REL234_LE, &limit)) {
+            printf("No solutions available in specified range %d-%d\n", rangemin, rangemax);
+            return 1;
+        }
+        limit++;
+    } else {
+        start = 0;
+        limit = count234(s->outputtree);
+    }
+
+    for (i = start; i < limit; i++) {
+        char buf[256];
+
+        o = index234(s->outputtree, i);
+
+        sprintf(buf, "%d", o->number);
+
+        if (pathcounts)
+            sprintf(buf + strlen(buf), " [%d]", o->npaths);
+
+        if (got_target || verbose) {
+            int j, npaths;
+
+            if (multiple)
+                npaths = o->npaths;
+            else
+                npaths = 1;
+
+            for (j = 0; j < npaths; j++) {
+                printf("%s = ", buf);
+                print(j, s, o);
+                putchar('\n');
+            }
+        } else {
+            printf("%s\n", buf);
+        }
+    }
+
+    free_sets(s);
+
+    return 0;
+}
+
+/* vim: set shiftwidth=4 tabstop=8: */